1. Field of the Invention
The present invention relates to a bi-directional drive motor having a force coil which is capable of moving in both an X and a Y direction. More particularly, the present invention relates to bi-directional drive systems for positioning objects such as a load platform for high speed machines and robotic devices.
2. Description of the Prior Art
High speed assembly machines such as those used in the semiconductor and electronics industry are presently available to perform various steps in the manufacture of finished products as well as the components and sub-assemblies for such products.
High speed automatic wire bonders and die bonders are presently available which perform the steps of bonding semiconductor chip to substrates and then connecting the terminal pads on a semiconductor chip or device to the lead out pad on conductors which connect the chip to other devices or circuitry. Both die bonders and wire bonders require that the substrate or device be moved relative to the bonding tool at each bonding point. In the case of wire bonders, the fine wire in a capillary or wedge bonding tool is bonded to a pad on the semiconductor chip and then moved to a second bond position at a lead out pad. It will be understood that this relative movement can be accomplished by moving a load platform on which the bonding head is supported or alternatively by moving the X-Y positioning table which supports the semiconductor device (or substrate) on a work station. U.S. Pat. Nos. 4,266,710 and 4,361,261 issued to Kulicke and Soffa Industries of Horsham, Pa. show automatic wire bonders which employ X-Y positioning tables. Each wire bond interconnection is completed in approximately 200 milliseconds which requires that the X-Y positioning table move to a new position in a fraction of the bonding cycle time. It is not sufficient that X-Y positioning table drive motors be fast, but they must also be extremely accurate. As semi-conductor devices become more dense, a larger number of terminal pads are required, the size of such pads has been reduced to an optimum in smallness commensurate with supporting a proper wire bond. If the accuracy of the drive motor and its encoder are limited, the pad size must be increased to assure that proper wire bonds are made. While the positioning of a carrier or substrate prior to die bonding is not as crutial time wise, the accuracy of positioning the chip is an important factor which does affect yields of proper wire bonds.
Heretofore, X-Y position tables such as those sold by Kulicke and Soffa Industries have employed a.c. and d.c. drive motors as well as large cylindrical coils operated as voice coil motors and linear motors to position X-Y tables. All of these prior art motors have been adapted to drive a load in one direction only as will be explained in greater detail hereinafter.
U.S. Pat. No. 3,771,034 shows and describes a coil which has two vertical partial portions and a lower horizontal portion suspended in a magnetic field provided by a permanent magnetic and a hollow core assembly. Depending on the direction of current in the lower horizontal coil a vertical force is applied to a bracket attached to a type carrier which is positioned vertically opposite a solenoid striker which also moves. No means are provided for moving to a desired position and stopping. The coil can only be moved up or down to a desired position by the structure described.
None of the prior art motors are adapted to efficiently move a large mass in both an X and Y direction, i.e. bi-directional, but are constrained to drive a load in a single direction. U.S. Pat. No. 3,437,482 and art cited therein disclose a magnetic positioning device for moving a marker in a direction which is not constrained to a single X or Y direction, however, such systems are not adaptable to position a load platform for high speed bonding machines.
Applicant has concluded that it would be extremely desirable to provide a bi-directional drive motor system for an X-Y positioning table or platform which is faster, more economical to build and capable of more accurate positioning of a load platform than systems known heretofore in the prior art.